The present invention relates to a magnetic disk apparatus capable of detecting a fault of a head thereof, and more particularly to a magnetic disk apparatus capable of early detecting a fault of a head of a type in which the width of the head is reduced.
The present invention relates to a method of detecting a fault of a head of a magnetic disk apparatus, and more particularly to a method of early detecting a fault of a head of a type in which the width of the head is reduced.
Magnetic disk apparatuses developed recently have been changed from thin film heads to MR (Magnetoregistive) heads in order to raise the recording density. However, the MR head is no resistant to static electricity as compared with the conventional inductive head, such as the thin film head. Thus, the MR head suffers from a problem in that the MR head can easily be electrostatically broken.
When the MR head is electrostatically broken, only a portion of the MR film is usually broken in place of complete breakage. If a portion of the MR film is broken, the output from the head is lowered and thus an error is committed. If the error rate is not lowered excessively, no practical problem sometimes arises. If a partial breakage of the MR film is enlarged, any signal cannot however be reproduced by the head.
The above-mentioned conventional technique has no method for detecting partial breakage (for example, electrostatic breakage) of the MR film for use in the MR head occurring during operation of the magnetic disk apparatus. Therefore, there is a risk that a user continues to use the apparatus without knowing the breakage of the MR film until critical breakage inhibits reproduction of a signal (reading of recorded data).
If the MR film becomes defective in a case where the MR head is used as a reading head, the characteristic of the reproduction output deteriorates. It leads to a fact that the accuracy of positioning the head deteriorates when the control of position of the head is performed.
When data is reproduced, deterioration in the positioning accuracy causes data to be reproduced from a data track in a state where the reading head is at an offtrack position (a position deviated from a designed position). Therefore, the reproduction output degrades from the rated level.
Since the reading head is positioned adjacent to a track near a required data track in this case, the influence of the recording magnetic field of the adjacent track results in noise to be intensified and increased owning to the crosstalk.
As a result, the S/N ratio which is the relationship between the reproduction output and noise degrades, thus causing the reading error rate to deteriorate. If the position accuracy deteriorates when data is recorded, data is written on the data track in a state where the writing head is at an offtrack position.
Since the writing head is positioned near the adjacent track, the writing head overwrites a portion of the adjacent track. Thus, the width of the adjacent track is undesirably reduced. When the reading head reads data from the adjacent track having a small width, the reproduction output is therefore lowered and the crosstalk is intensified. As a result, read errors are committed excessively.
In general, it is difficult to make the sensitivity distribution of the magnetoresistance effect of an MR film of an MR head to be uniform and to obtain an ideal offtrack profile (OP). The foregoing problem arises in a case where the MR film has not been formed into single magnetic domains when the MR head has been manufactured; or the single domain state of the MR film is disordered owning to an electrostatic discharge (ESD) or excess current load (EOS). Thus, so-called Barkhausen noise (BHN) is generated.
Another case is considered in which a portion of the MR film becomes defective after the MR film has been used for a long time near its lifetime.
Handling of BHN among the above-mentioned factors greatly affects the actual performance of the hard disk drive. A fact has been confirmed that BHN appears/disappears when the MR film is stimulated with a magnetic field or temperature.
That is, if the MR head, which is the reading head, has BHN during the operation of the hard disk drive, BHN sometimes disappears owning to an influence of a magnetic field generated by a writing current for the writing head or a sensing current of the MR head. Inversely, the influence of the magnetic field or the atmospheric temperature sometimes causes BHN, which has been allowed to disappear, to again appear.
When the MR head is, as the reading head, employed in the conventional magnetic disk apparatus, occurrence of an abnormal state causing the linearity of the offtrack profile (OP) of the MR film to deteriorate results in accuracy of controlling the position of the head being allowed to deteriorate. In this case, the reading error rate deteriorates, and the performance degrades in the worst comes to the worst such that data recorded on the disk will be erased.